December 12, 2017

What causes infertility? The brain, of course.

With the discovery in 2013 that the ovaries weren’t the only producer of estrogen, researchers at the Wisconsin National Primate Research Center (WiNPRC) wanted to know how estradiol, the type produced by the hypothalamus region of the brain, affected the estrogen feedback loop.

This hormonal mechanism is the back and forth communication between the brain, pituitary gland and ovaries that regulates the menstrual cycle. The brain and pituitary gland tell the ovaries to produce estrogen. Estrogen then tells the brain and pituitary gland to release hormones. Those hormones then tell the ovary to release an egg. But after the discovery that the brain also produced estrogen, scientists at the Wisconsin National Primate Research Center wanted to know how these two sources of estrogen interact.

Using rhesus macaques as test subjects, they temporarily stopped their ovaries from producing estrogen. They also implanted a capsule under the monkeys’ skin that would release estradiol. The result? The brain and pituitary gland released only 30 percent of the luteinizing hormone necessary to begin ovulation.

Then, the researchers repeated the process, but this time, they blocked estradiol production in the hypothalamus. But without the estrogen produced by the brain, the hormones weren’t concentrated enough to release an egg.

“The ovarian estrogen starts the [hormone] surge, but the brain estrogen allows the surge to continue,” says Brian Kenealy, a researcher at the WiNPRC.

“This shows the brain’s estrogen is a huge helper, necessary for the release of an egg that makes pregnancy possible,” says Ei Terasawa, a pediatrics professor at the UW-Madison School of Medicine and Public Health and senior scientist at the Wisconsin National Primate Research Center. “We have to modify our concept of the feedback loop.”

For women struggling with infertility, this finding may unlock future treatments. For now, it’s a step forward in our understanding of the estrogen feedback loop.

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